I was pretty surprised myself, but it's not necessarily "hell freezing over" as some have put it. This could be nothing more than an attempt to regain some favor among FOSS enthusiasts, or an attempt to increase use of their Hyper-V products.

It's a nice gesture, but for all I know about Hyper-V (which admittedly is very little), it's a deliberate strategy with an ulterior motive.

edit: After some quick reading on Wikipedia, I'm more convinced that what I said above is true.